Kennen vs. Wissen?
Just a quick question: the infinitives Kennen & Wissen both mean "to know". When do I use which one?
Kennen: You can recognize something or somebody. You know a person because you have seen the face and learned the name. Or a movie. If you really know someone ("ich kenne ihn wirklich") then you assume that you know how he will act or what motivates him but that is an extended meaning of kennen. Kennen mostly is superficial. "Ich kenne den Bürgermeister" ("I know the mayor"). You don't express that you know him inside out but you have contact to him (and often when people state such the other person doesn't know them, otherwise they would use more specific phrases like "we are friends").
Wissen: You have specific knowledge. You know facts, relations, causes. You know how a machine works. You know specific data points (e.g. 0.42°).
This is a good description. Context helps a lot. You can say "Ich kenne Paris" but you can't say "Ich weiß Paris". In general you cannot put "wissen" together with people or places but only facts.
"Kennst du Hulk Hogan?" -"Nein, aber ich weiß wer das ist."
"Do you know Hulk Hogan?" -"Not, but I know who he is".
So as landsend has explained, you can use "kennen" with a person and a fact, but "wissen" only for 'data'. In the example that would be the information that the person in the picture is Hulk Hogan, but you (probably) never met him and therefore can't say you know (kennen) him.
The difference can be seen in one example:
- Ich kenne sie. Ich weiß, wie sie ist. = "I know (acquainted with) her. I know how she is."
Also, there is one expression which naturally takes wissen:
- nicht mehr wissen = "to not remember" (lit. "to no longer know").
It is worth emphasizing that it is rarely either kennen OR wissen. In many situations you can use both but they mean slightly different to very different things.
For those who like grammar-like explanations:
- kennen = (semantic) entities, (structural) especially names or people or nouns, (state) being acquainted with something
- wissen = (semantic) verb-based information, (structural) especially clauses, (state) knowing a fact, often implicitly answering a W-question: wie, was, wer, welche, etc.
If in doubt, always fall back to structural usage. This will sound natural most of the time.
It helps to memorize "kennen" as to be familiar with, to be acquainted with. If you can use one of these two instead of to know, you usually need "kennen".
If you're familiar with Spanish and/or may learn it in future, kennen corresponds to the Spanish conocer, and wissen to saber (not as in light).